An uplink adaptive technology in a Long Term Evolution (LTE) system is that: a base station device estimates quality of a Physical Uplink Shared Channel (PUSCH) of a user equipment (UE) according to quality of an uplink Sounding Reference Signal (SRS) of the UE, and chooses a Modulation and Coding Style (MCS) matching the UE channel quality when scheduling the PUSCH. In particular, the base station device estimates the Signal to Interference plus Noise Ratio (SINR) of the uplink channel quality of the UE according to the uplink SRS of the UE, and determines that the SINR obtained from the SRS measurement approximately equals to the SINR of the PUSCH of the UE, thereby determining the MCS index corresponding to the PUSCH of the UE. Moreover, when scheduling the UE, the base station device can determine the amount of Physical Resource Blocks (PRBs) to be scheduled for the PUSCH according to the MCS index and a data volume of the UE to be transmitted.
The MCS estimated according to the SRS is considered to be the MCS of the PUSCH, but in certain cases, the former does not equal to the latter, A terminal device is restricted by a maximum transmission power, but an SRS signal and a PUSCH signal may not be restricted by a maximum transmission power simultaneously, so the transmission power of a single PRB of an SRS signal and of a single PRB of a PUSCH signal may be different. For example, an SRS is provided with 96 PRBs; when a UE is at a distant point, due to large path loss, the uplink transmission power is restricted, and the actual transmission power of a single PRB falls short of expected power; whereas when the UE schedules a PUSCH, due to the small size of a data volume to be transmitted, the amount of PRBs actually to be scheduled for the PUSCH is small, so the transmission power of a single PRB of the PUSCH is higher than the transmission power of a single PRB of the SRS, namely, SINR of the PUSCH is greater than the SINR of the channel of the SRS; in other words, the SINR estimated according to the SRS cannot represent the SINR of the PUSCH, so it is inappropriate to equate the MCS estimated according to the SRS with the MCS for PUSCH scheduling.
Use of the same MCS index, no matter how many PRBs are finally scheduled for a PUSCH, is not always proper. When transmission power of the PUSCH is maximized, the actual received power of a single PRB does not equal to expected received power; when a different amount of PRBs of the PUSCH are scheduled, the transmission power of a single PRB is different, which is to say, the SINR of the PUSCH is different when the amount of PRBs is different. For example, 50 PRBs are scheduled first, and the power of each PRB is 6 dBm; 25 PRBs are scheduled later, and the power of each PRB is 9 dBm. If the same MCS is used in scheduling, the SINR used to determine the MCS would be different from the actual SINR of the PUSCH; for the PUSCH with transmission power of each scheduled PRB being 6 dBm, the MCS index used may be too high, whereas for the PUSCH with transmission power of each scheduled PRB being 9 dBm, the MCS index used may be too low.
If the amount of scheduled PRBs of a PUSCH is not restricted, receiving performance of a PUSCH at an edge of a ceil cannot be ensured. When a UE is at an edge of a cell and has a large path loss, and the uplink transmission power is restricted, the scheduled MCS index may be set to 0, but if the amount of scheduled PRBs of the PUSCH of the UE at an edge of a cell is not restricted, and 96 PRBs are scheduled, then received power of a single PRB of a base station device may be very low, and decoding may not be correct even if the scheduled MCS index is 0.